Problem: Suppose the area of a circle is ${49\pi}$. What is its diameter?
Explanation: ${K = 49\pi}$ ${d = 14}$ First, find the radius: $K = \pi r^2$ , so $r = \sqrt{K / \pi} = \sqrt{{49\pi} / \pi} = {7}$ Now find the diameter: $d = 2r = 2\cdot {7} = {14}$.